The present invention relates to pressure switches and particularly pressure switches of the type wherein the switch exhibits make-before-break characteristics on increasing pressure and also make-before-break actuation characteristics upon decreasing pressure. Switches having this type of actuation characteristics find application in automotive air conditioning systems where it is desired to control the energization and de-energization of the refrigerant compressor clutch in response to changes in the pressure of the vaporized refrigerant circulating in the system.
Typically, automotive air conditioning system pressure switches employ a pressure-responsive diaphragm acting against a movable piston to provide the necessary actuating force for operation of the electrical switch mechanism to control the compressor clutch. However, it has been found in pressure switches of this type that the required movement of the piston produces undesirable amounts of movement of the diaphragm in the boundary regions thereof. This movement has ultimately resulted in fatigue failure of the diaphragm and reduced service life of the pressure switch.
It has thus been desired to find a way or means of controlling the movement of a pressure-responsive diaphragm in a pressure switch in a manner that will produce long service life in terms of number of cycles of the switch and yet provide the desired make-before-break binary type actuation of the switch over a broad range of sensed pressures. It has also been desired to devise such a binary action pressure switch which has a minimum of parts or components and lends itself to high volume mass production techniques and has a resultant low manufacturing cost.